A laser oscillator for laser processing application may include a couple of oscillator modules each operable to oscillate a laser beam, so that the laser beams oscillated by these oscillator modules can be collected for output. Each of such oscillator modules by itself can adequately provide for a laser oscillator, as well. Such oscillator modules are often combined to provide for a laser oscillator of a significant output that cannot be achieved with a single oscillator module, and a number of the oscillator modules may be employed according to the required output power of the laser oscillator. In sheet metals cutting application, for example, a large number of oscillator modules are associated with a laser processing machine to meet the demand for a greater cutting capability.
Conventionally, to adjust the output power of a laser oscillator that includes a plurality of oscillator modules, control is applied such that all of the oscillator modules are adjusted by the same proportions. For example, to adjust the output power of a laser oscillator to 50% of its maximum rated output, control is applied such that all of the output powers of the oscillator modules are regulated to 50% of their maximum rated output (see JP Laid-open Patent Publication No. 2003-037316).
When the output power of a laser oscillator is set low relative to its maximum rated output, a laser processing operation becomes unstable. Normally this is due to poor control resolution of the output of a laser oscillator; for example, control of a laser oscillator within the range of less than 10% of its maximum rated output is very difficult. This, in turn, makes it difficult to perform fine adjustment of its output in response to changes in the designated value for the output power that occur during a laser processing operation. In this way, considerable output fluctuations may occur during the processing operation. As such, fine adjustment is difficult and stable processing quality cannot be achieved. This also applies to a laser oscillator including oscillator modules whose output powers can be designated to select levels. A laser processing operation stabilizes when the designation is to a higher output power (e.g., 40% of the maximum rated output), better than when the designation is to a lower output power (e.g., 10% of the maximum rated output).
In laser cutting of a sheet metal, a correct curve shape requires the movement of a laser beam at a speed lower than when cutting a linear shape. When moving a laser beam at a lower speed, it may be necessary to reduce the laser output power because otherwise the heat input from the laser beam into a material undesirably increases. However, the aforementioned limit on the fine adjustment capability does not allow for regulation of the laser output power to a proper level. The resulting overheating or inadequate heat input jeopardizes a stable processing operation.